Internally heated drier



W. C. GOSS .h me 9, 1942.

INTERNALLY HEATED DRIER Filed A rii 19, 1959.

' INVENTOR VVOATH 6 BY Gan/- ATTORNEY Patented June 9, 1942' UNITEDSTATES PATENT OFFICE wfifilfiiffiztf. Application April 19, 1939, SerialNo. 258,703

'I'Claims. (or sea-1s) This invention relates to' improvements in driersand has reference more particularly to an equipment designed for thedrying of comminuted material preparatory to its being bri quetted.

More specifically stated, the invention relates to driers for cellulosicmaterial, and comprises a continuous, circuitous tube into which thematerial to be dried is delivered, and with which tube a fan isassociated for creating a violent circulation of material around thecircuit, and wherein a quick and thorough drying operation of thematerial is eflected by the application of a blast of hot gases into thetube; the present invention being somewhat in the nature of animprovement upon the disclosures in United States Letters Patent No.l,985,250,'issued Die-- cember 25, 1934, to O. P. M. Goss and Worth C.

It is the principal object of the present invention to provide a drieroi the character above stated that will eilect its intended functionquickly and thoroughly; which may be employed to either dry and heat thecomminuted material to a condition desired for briquettingby a hotprocess, or may be employed to warm the material and regulate themoisture content thereof so that it may be briquetted under theplasticizing action of the contained moisture.

It is also an object of the present invention to provide a drier of aportable character and of such construction that it is adapted to beingtransported in connection with apparatus designed for the briquetting ofstraw and the like.

Another object of the invention resides in the provision of a novelmeans for extracting dried material from the mass as circulated in thedrying tube under influence of the propelling fan, and in the provisionfor automatically controlling the said means in accordance with the loadon the propelling fan.

' shown, themotor has direct connection with the -fan shaft, and thereis a ball governordevice 5,

operated by the motor for a purpose presently explained in connectionwith the control of the discharge of dried material from the tube.

The material to be dried, such as comminuted straw, sawdust or othercellulosic material, is delivered. into the tube 1, at a point adjacentthe inlet side of the fan housing 2, through a feed tube 8.- Preierably,the feeding of the material is'efiected by the action of an Archimedeanscrew I, which, as here shown, is contained in an enlargement t .of thetube 6 and operates to keep the tube 6 packed with the comminutedmaterial, so that the material will operate effectively as a closuremeans whereby outside air is kept from entering the tube I through thisinlet, and gases inside the tube I are kept from escaping therethrough.

The material to be dried may be delivered to tube 6 and the screw I byany suitable means.

Other objects of the invention reside in the Fig. 1 is a diagrammaticillustration of a drier embodying the presentinvention.

Fig. 2 is a similar view illustrating a modified, or alternativeconstruction.

Referring more in detail to the drawing-- Preferably, it would bereceived at the receiving end of the feed screw directly from the deviceby which it is reduced to its desired comminuted livery-tube 8.

Should the comminuted material, in its entrance into the tube I from thetube 6, be packed v by reason of the feedim-g: pressure exerted by screwI, it will quickly be broken up upon entering the housing 2, by theaction of the fan 3, and is then easily carried In suspension about thetube I by the gas current. 1

When the present apparatus is putto use as a high temperature drier, thedrying gases in the tube I are preferably maintained at a constanttemperature 01 approximately 430 Fahrenheit.

In the construction as shown in Fig. 1, I designatesthe main drier tubewhich would be of substantial diameter and length, and continuone inthat it forms a closed loop, or circuit.

Interposed in the tube, as a part of the circuit. II) of a pipe Thisheat is derived by use of a heating device, such as an oil burner, ofsuitable kind, as designated' at I0,.arranged to deliver its hot inertgases through a blast tube IIIa into a tube II, which in turn,discharges directly into the main tube I.

As will be noted in the drawing, there is an automatic separator deviceassociated with the drier tube. This .separator comprises a closedhousing I2 containing a centrifugal separating i'an I3. The housing I2is connected by means II with pipe I, to receive material from materialto one point of discharge that is,

V in their passage to the pipe I, are mixed with the housing I2 past theoil burner where the blast tube Ina enters it; then the tube II curveslaterally and opens into tube I in the direction of the flow of gasestherein.

The fan I8 may be driven by any suitable means, and the function of thefan is to separate the dried material from the gases diverted into thehousing I3, through tube II, and to deliver the hot gases again into thedrying circuit through the tube II, and to discharge the dried materialthrough a tube It leading from the fan housing I2 into a hopper It fordelivery from the hopper to storage or to a point of use, such as abriquette press. 'This separating fan might be replaced by a separatingcyclone of conventional design.

It will be understood that since the discharge end of tube Ii enterstube I in the direction of flow oi gases in. the latter tube, there willbe no tendency of back. pressure in tube H, but rather, suction will becreated to draw gases from the housing I2 of the separating device.Also, since the pipe It leads from the pipe I at the sheltered side of abend, or turn, therein, it is necessary to provide means 'for divertingthe dried material thereinto. In the present instance, I haveillustrated use of a baiiie plate or damper I8 for this purpose; theplate extending inwardly from the inside wall of tube I Just beyond theentrance into pipe It, and by reason of its extending into the tube I,it operates as a deflector for diverting the material that strikes it,into tube I4, and thus to the separating fan. I

In the event that the material being dried has an excessive moisturecontent so that the oil burner is incapable of maintaining thetemperature at the proper degree in the tube I, the speed the feed screwI is automatically reduced or temporarily stopped under the control of asecondary thermostat 28, which would shut oil the feed of fresh materialthrough the screw I.- This would only occurif the temperature in thetube I drops below 420 F. When the temperature again rises to 430 It,the feeding of fresh material is again resumed through the screw I. Itis also contemplated that the mill'8 and the conveyor 9 be controlled bythis same thermostat, 23, so that its speed of operation will be reducedor stopped, accordingly, with the feed screw I.

The plate or damper I8 is slidable in a guidespasms V the latter, andthe return tube II leads from the hot gases from the oil burner toreduce the temperature of the latter, to not more than 700 F.

By reason of the high degree of heat employed in the drying tube I, andthe fact that moisture fan housing 2.

contained in the material being dried will be converted into steam bythis heat, it is necessary to provide a steam outlet for the system andthis preferably is from pipe II as herein designated at 24. Also, it isdesirable that the temperature of the gases in tube I be keptsubstantially at a constant degree of temperature and Ifor this purpose,I have installed a thermostatic device 21 in a side wall of tube I, atthe inlet side of This thermostatic device could be of -any conventionaltype, as now universally used in heating plants for burner control, andwould be connected electrically or otherwise in the oil burner controlsystem to cut oil? the heat 'when it reaches a predetermined degree, andto turn it on when the temperature falls to another predetermineddegree.

A modification of the system above described is illustrated in Fig. 2,and the modification resides principally in the means for applying heatto the drying tube I.

Under certain conditions, it will be desirable to use waste flue gasesas the heating medium. However, since these gases might not always beinert chemically, it would be extremely dangerous, from the standpointof dust explosions, to

' inject them into the drying tube I. Therefore,

it is desirable that these waste flue gases be utilized exteriorly oftube I by applying them within a jacket 30 surrounding tube I, as shownin Fig. 2; such a jacket being substantially like that shown in thepreviously mentioned patent.

In this way, the drying tube would be heated externally and the materialto be dried would be circulated in a pure atmosphere of super- I9 andhas a, rod 20 at its outer end connected I accomplished through a pipe25 under control of a valve 26; the valve being controlled by thegovernor-device 5 connected with the motor 4.

Thus, when the motor is slowed down, by reason of too rapid feeding ofmaterial-into the circulating tube, the fan 3 will be slowed down, andthe deflector plate will project further into tube I accordingly to takemore material fromthe tube.

The separating device I3 isof standard construction, and by itself formsno part of this invention. Briefly, it is of that character wherebycentrifugal action operates to deliver the dried to the tube I5, leadingto hopper I8, and the air or gases are forced to another point ofoutlet. In this instance, the gases diverted-to the housing ii arereturned to the system through the pipe II and heated steam.

When the heat is thus applied, a slight steam pressure is maintainedinside the'dryer'to preclude the possibility of the entrance of any airor gases into the drying tube, this being to prevent dust explosions. Toinsure this pressure, steam'may be admitted from a source of supply 32under control of an automatic solenoid valve 33, and in practise thissteam pressure in the drying tube would never be higher than oneeighthpound per square inchabove atmospheric pressure.

In the case that it is desired to introduce waste flue gases directlyinto the drying tube I, this may be done with safety it precaution istaken to insure the comparative inertness of the gases before they enterthe tube. For example, steam might be added to the gases under thecontrol of a regulating carbon dioxide meter, or the gases might bepassed'through an additional furnace where any oxygen present would becaused to combine with carbon, thus forming additional carbon dioxidegas. In any event, a regulating carbon dioxide meter would be advisabletouse as an' insurance of the inertness of the flue gases.

. Assuming the apparatus to be so constructed, its use would be asfollows:

Comminuted material to be dried will be delivered from its source ofsupply 8 into tube hopper 6' by the conveyor 9 for delivery by theArchimedean screw I through the tube 6 into the tube I. As this materialis thus fed into the tube I its packed condition in the tube 6 willpreclude the entrance of any air to the system and also will prevent anydischarge of gases from the system through this feed tube passage. lumpsof comminuted material that might be forced into the tube I by reason ofthe pressure ernor 5. 'I'heoperation baflie will be extended valve is toprevent any of the feed screw will be readilybroken up by the action ofthe clrculatingfan 3.

When the apparatus is used as a high 'texnperature'drier, a constanttemperature of approximately 430 F. will be maintained in the tube Ithrough the control of the oil burner III by the thermostat 2'! that isinterposed inthe tube I. The hot gases delivered directly from theburner into the tube II will be tempered by mixture with a large volumeof spent gases that are discharged from the separator housing I2 intothe tube II for delivery thereby into the main drier tube I, at atemperature not in excess of 700.

As the comminuted material is thus violently circulated within the tubeI, by the action of the fan 3, it will be quickly and efl'ectively driedand the dried material will be discharged from the tube to the separatorby the diverting action of the damper or baflle I8. .Thematerlahwhichbe-.- comes dry and dustifled, is deflected into pipe I4 by the baffle,due to the fact that the heavier, undried material will be thrown to theoutside of the bend of the tube and the lighter material forced to theinside, where-it contacts with the baflie. The disposition of the bailiein the bend of the tube i, as illustrated, facilitates this mode ofseparating the dried material from the undried material in the tube I,and makes possible the present control by the governor 5.

Material received along with the hot gases within the separatingapparatus Ii! is diverted by reason of centrifugal action, to the outletI5 leading to the hopper I6, while the spent gases are directed intotube II for return to the system after being mixed with the hot gasesfrom the oil burner.

rial, the deflecting baflle will be pulled in or extended inaccordancewith the speed of operation of the. fan 3. This of comminutedmaterial in suspension in the air in the drier tube I at any time andthe regulation of the deflecting baflie is accomplished through theconnection described, with the govis such that when the slowsdownslightly, which may be due to load of materialin the drier tube, thefurther into the tube, thus causing the discharge of more driedmaterial. If, on .the other hand, the fan is spedup, the baiile will beretracted'accordingly, thus allowing a greater quantity of comminutedmaterial to remain in suspension in thedrier tube-- fan '3 heavy '15..the apparatus is to be usedto prepare material ior briquetting underwhat might be tent, steam will be generated suflicient that a part willbe expelled through the outlet port '24 provided.

When the drier is used to prepare. material for this so-called plasticprocess, it tends -to have a larger tonnage capacity than when it isused {to dry or heat material to an extremely high temperature.

If the moisture required to suppl the required moisture content is notavailable .as steam, a

small water spray may be introduced into the drier tube at a convenientpoint to add mois-.-

ture that will ,turn'to steam Iuncler the action of hot gases.

Where the drier is to be used for the purpose of drying rather coarsematerial, such as wood chips or comminuted cornstalks, there is a par--ticularly desirable actiondnherent in the operation of the apparatus.This function is one of comminution of the material as it is drivenaround and around the drying duct Each time alarge piece of materialpasses through the fan,

small pieces will be broken therefrom so that a large piece of materialgradually decreases in size. 'It is an inherent property ofthe de-.flecting bafiie that only small pieces of material 1 will be deflectedinto the separating device, due

. 40 To prevent overload of the drier with mateis to regulatethequantity The steam discharge outlet 24 from the tube II will be providedwith a suitable yieldable damper or valve which is so regulated as toopen or close, to asreater orv lesser degree, by the pressure inside oftube tube; also, to vent the necessary quantity of steam and spent gasfrom the drier. I Thus, the danger of explosion is minimized as with ahigher II. The purpose of this f intake of air into the atmosphere,consisting of steam," nitrogen and carbon dioxide. make impossible q pent.

This inert gas obviously would any explosive action inside the to thefact that the mass of any large pieces of material in the air streamwill carry them to the outside of the bend in the tube by centrifugal Iforce, oh the inside of whichthe' deflecting baflie is set. Small lightpieces of material, however, are not thrown-to the extreme outsidesection of the, duct and will be caught by the. deflecting baflie andthen'separate from the gas stream. Thus, the drying apparatus not onlycauses a reduction.in moisture content of any material,

fed thereinto, but also reduces the size of any large particles whichmay be present in the material being dried. This property of comminutionmay-be regulated by the specific arrangement of the deflecting baflle.If extremely flne materialis desired, the baflie is completely hidden onthe inside bend of the drying duct. If it is desired to permit egress oflarger pieces, then the separating baffle maybe nearer the intake sideof the bend in the duct.

Driers of this character may be constructed as. either portable orstationary equipment. In

either instance, they aflord quick and thorough drying of material andprovide also for a control of moisture content when such is desirable.The feed 01. material and the control of heat supplied by the burner isautomatic and, as a whole, the equipment is relatively simple andinexpensive. I 1

Havingthus described my invention, what I"- claim as new therein anddesire to secure by Letters Patent is: v i. Ina drying apparatus, acontinuous tubular duct, means for feeding material'into the ductfor-drying means for supp y g hot, drying gases into the duct, meansinterposed in the duct for the drying gases about the duct with p pellin-a velocity whereby the material will be carried in suspension therein,a motor for the prope in means, a device outside the duct for theseparation of dried material from its carrying gases,

.a by-passing mbe leading into said device from into the separatingdevice, and a device operatively connected with the baflie, andresponsive to changes in load placed on the motor to djust the baiiiefor, the deflection of a greater or lesser amount of gases in accordencewith the change in load placed on the motor.

2. In a drying apparatus, a continuous tubular drying duct, means forfeeding material into the duct for drying, a fan interposed in the ductand operable for propelling the duct gases about the circuit at avelocity whereby the material will be carried in suspension therein, amotor for driving the tan, means for delivering hot drying gases intothe duct, a device outside the duct for sep- -arating the dried materialfrom the drying gases, a connecting tube through which a part of thestream of circulating gases and contained material may be by-passed fromthe duct to the said device, a gas return connection from the device tothe drying duct, a movable baiiie in the duct for the diversion of agreater or lesser part of the stream oflcirculated gases through thesaid connecting tube to the separating device, a governor deviceoperable by and responsive to changes in load placed on the motor, andmeans actuated by the governor device to control the adjustment of thebaiiie for the diversion of more or less material in accordance with thespeed of the fan.

3. In a drying apparatus, a continuous tubular duct, means for effectinga controlled feeding of material into the duct to the exclusion ofoutside air, propulsion means interposed in theduct and operable for thepropelling oi the duct gases about the duct at a velocity to carry thereceived material in suspension therein, a device-outside the duct forthe separation of dried material from the gases, atube connecting theduct and said separating device, means for diverting a part of thecirculated stream of gases and material from the ductthrough said tubeinto said separating device, a pipe connection for the return of thegases from said separating device into the duct, an electricallyoperated gas burner having a blast tube directed into the gas returnpipe to supply the duct with hot gases for the drying of materialtherein with an incident generation of superheated steam, an electriccircuit for the burner, and a pressure relief valve in the returnconnection.

4. In a drying apparatus, a continuous tubular duct forming a dryingcircuit, means for eilecting a controlled feeding of comminuted,moisture containing material into the duct to the exclusion of outsideair, a fan interposed in the duct and operable for the propelling of theduct gases about the drying circuit at a velocity suiiicient to carrythe received material in suspension therein, a motor for driving thefan, means operable for the injection of hot, inert gases of combustioninto the duct at a'temperature (or heating the circulated gasesfordrying thematerial with an incident creation of super-heated steam, apresasaasos sure relief valve for the a device outduct and said device,a movable baiiie in the duct .for diver-ins a part of the stream ofcirculated gases to more or less amount. from the drying circuit intothe said tube to the said device, a governor operable by and responsiveto changes in load placed on the motor, and means controlled by thegovernor for adjusting the position of the bails.

5. In a drying, apparatus, a continuous, tubular drying duct. having anangular bend at one point, means for eflecting a controlled feeding ofcomminuted material into the duct to the exclusion 'of outside air, afan interposed in the duct and operable for the propelling of theductgases at a velocity whereby the received comminuted material is carriedin suspension therein a motor for driving the fan. a device outside theduct for the separation of dried material from its carrying gases, aby-passing connection leading into the said device from the shelteredside of the bend in the drying duct, a gas return connection from theseparating device into the drying duct and opening into the latter insuch direction as to cause suction to be created therethrough, a baiiieadjustably mounted in the drying duct and movable to divert a greater orless proportion of the stream of circulated gases into the separator, agovernor operable by and responsive to changes in load placed on themotor, means controlled by the governor for adjusting the position ofthe baiiie, and a gas heating burner having a'blast tube opening intothe gas return connection for the discharge of hot inert gases into thestream of return gases. to heat the circulated gases to high temperaturefor the drying of material with an incident generation of super-heatedsteam from the moisture contained in the material, and a pressure reliefvalve in the return'connection for exhaustion of steam.

6. A device as in claim 5 including thermostatic means and meansoperable under control or the thermostatic means to control the burnercircuit so as to maintain a substantially constant drying temperature inthe duct gases.

7. Inva drying device, a continuous, tubular drying duct, means-foreilecting a controlled delivery of comminuted material into the duct fordrying,'means including a driving motor for effecting a circulation oigases in the duct at a velocity whereby the material will be carried insuspension, a device outside the duct for separation of material fromgases, a by-passing connection between the drying duct and said device,a gas return connection from said device to the drying duct, anadjustably mounted damper in the duct for diverting a part of the streamof circulated-gases to said by-passing connection;

said duct having abend therein slighthr in ad-, vance of the by-passingconnection whereby to effect a centritugal deflection of the materialcar-' WORTH 0. dose.

